A. Field of the Invention
This invention relates in general to improved components of an automatic temperature control system for automobiles.
B. Description of the Prior Art
Automatic temperature control systems were first introduced in about 1964 in the United States and are now available on most large size cars. In the systems heretofore, the components of the system have been scattered throughout the car, being interconnected by vacuum and wiring harnesses. One of these systems, for instance, has a main component grouping on the power servo, with other hardware located on the dash control, in ducts, on the air conditioning case, and in the engine compartment. Another has many components grouped on the heater-air conditioning case, with other components on the dash control, under the dash and in the engine compartment. These systems are generally complicated, difficult to install and maintain, expensive to produce and inaccurate.
The components of such systems and their function is as set forth below:
1. Sensors--to sample in-car and ambient temperature;
2. Transducers--to convert the sensors' output to a control signal;
3. A power servo--to convert the control signal to a stroke, thereby driving program switches and a temperature door. Bimetal sensors have been used to sense temperature changes and provide a signal responsive thereto for many years. However, the signal from such a sensor is very small and is rarely able by itself to provide the necessary force to activate a mechanical or electrical system of which the sensor is a part;
4. Program switches--to control system functions such as air discharge location, blower speed, recirculation, water valve, on-off function, etc.;
5. A temperature blend door--to modulate the air discharge temperature from the heater-air conditioning system;
6. Dash controls--contains levers used by the driver of a car to adjust and set the system to the desired mode and condition of operation;
7. Selector switches--operated by the dash controls;
8. Cold engine lockout (CELO) valve--to delay the system operation in its heater mode until the heater core is warm;
9. Compressor ambient switch--to control the compressor operation as a function of the ambient temperature;
10. A water valve--controlled by a program switch to turn water off to the heater core under maximum cooling conditions; and
11. A resistor block--contains a dropping resistor for fan speed control. This works in conjunction with the program switches.
There are many problems associated with these systems.
In operation, these systems generally have two sensors which individually sense the ambient and in-car temperature and convert these readings to either electronic or mechanical signals. The ambient signal is used to bias the in-car signal and the single output is used to control the operation of the system. The appropriate temperature is generally supplied by the operation of a temperature blend door whose opening and closing regulates the heat and air conditioning supplied from the heater and air conditioner.
Since the sensors are often mounted at the end of long tubes supplying the in-car and ambient air, error in the sensing apparatus is often introduced by the air passing through long super-heated stretches which bias the temperature of the incoming air. For instance, the in-car air is often sampled by letting air enter a tube which is underneath the dash. By the time the air reaches its sensor near the fire wall, the temperature of the air in the tube has often reached an elevated temperature to that of the original air by reason of bias occurring when the air passed through heated areas under the dash. This problem has sometimes being corrected by placing the sensors at the spot where sampling air was taken in, but this requires long electrical leads and electrical conversion signals for changing the temperature of the air sensed to an appropriate electrical value.